Method of apparatus for removing tramp metal from polyethylene

ABSTRACT

A method for separating tramp metal particles from a first stream of gas carrying polyethylene particles, which comprises delivering such first stream tangentially at high velocity into a chamber of large volume wherein all particles settle out, and withdrawing from said chamber a second stream of high-velocity gas having suspended therein only particles of polyethylene. The method has particular utility when intermittent flow is involved. The apparatus for performing the method comprises an upstanding cylindrical chamber of large volume, a first conduit having an outlet connected tangentially into the chamber at a position between the top and bottom for supplying the first stream thereto, and a second conduit leading from near the top of the chamber and having an entrance below the top and above said outlet for conducting the second stream therefrom.

United States Patent 1151 3,642,115 1 Bartles et a1. 1 1 Feb. 15, 1972 [54] METHOD OF APPARATUS FOR 794,789 5/1958 Great Britain ..209/144 VIN TRAMP METAL FROM 922,497 6/1947 France ..2()9/155 POLYETHYLENE [72] Inventors: Edward C. Bartles; William R. Matthews, both of Rochester, NY.

[73] Assignee: Eastman Kodak Company, Rochester,

[22] Filed: Oct. 21, 1969 [21] Appl. No.: 868,072

[52] US. Cl ..209/l33, 209/144 [51] Int. Cl [58] Field of Search ..209/l44, 133, 132,21 1, 155

[56] References Cited UNITED STATES PATENTS 956,817 5/1910 Morscher ..55/345 418,834 1/1890 Allington et al... ...209/144 1,031,862 7/1912 Morse... ..209/l44 2,471,326 5/1949 Hoyt ..209/144 FOREIGN PATENTS OR APPLICATIONS 817,342 7/1959 Great Britain ..209/211 Primary Examiner-Frank W. Lutter Assistant ExaminerRalph J. Hill Att0rneyWalter O. Hodsdon and Henry M. Chapin [57] ABSTRACT A method for separating tramp metal particles from a first stream of gas carrying polyethylene particles, which comprises delivering such first stream tangentially at high velocity into a chamber of large volume wherein all particles settle out, and withdrawing from said chamber a second stream of highvelocity gas having suspended therein only particles of polyethylene. The method has particular utility when intermittent flow is involved. The apparatus for performing the method comprises an upstanding cylindrical chamber of large volume, a first conduit having an outlet connected tangentially into the chamber at a position between the top and bottom for supplying the first stream thereto, and a second conduit leading from near the top of the chamber and having an entrance below the top and above said outlet for conducting the second stream therefrom.

3 Claims, 3 Drawing Figures FA/V 25 29 CONTROL RECEIVE? 33 35 5' X TRUDER PATENTEDFEB 15 I972 S/LO " "R ii RECEIVER 33 E X TRUDE/i EDWARD C. BARTLES WILL/AM R. MATTHEWS 4 INVENTORS A 7' TORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention Our invention relates to a method of and apparatus for pneumatically transporting from a source of supply to a locality ofconsumption particles ofa material such as polyethylene.

More particularly, our invention resides in a novel trap construction for removing relatively dense tramp metal from relatively much lighter particles, such as polyethylene pellets, carried in a stream of air or other gas.

2. The Prior Art Cyclone separators have long been known for continuously separating relatively dense particles from lighter particles being pneumatically transported. For example, such separators are described in U.S. Pat. Nos. 911,258 and 2,042,203 wherein a stream is introduced near the top of a chamber and then leaves through a conduit having its entrance at a lower level. While devices as in US. Pat. No. 3,042,203, having a closed bottom, are operable when there is continuous flow, with interrupted flow they tend to fill up with solid particles each time flow ceases and cannot then be restarted unless the bottom is first opened and the particles dumped. When the bottom is open, as in U.S. Pat. No. 91 1,258, much material is lost out the bottom continuously. U.S. Pat. No. 2,540,348 shows a separator wherein air enters the bottom of a separator chamber and particles leave through a conduit having a very large diameter entrance flush with the top of the separator, but this also would clog each time the gas flow stops, and then could not be restarted (due to settling of the particles in the lower chamber where they would cover the air inlet, and to the low velocity of the gas at the top of the chamber).

We have endeavored without success to obtain from industrial suppliers a trap that will operate dependably with an intermittent flow of pellet-laden air.

SUMMARY OF THE INVENTION In accordance with our invention we have provided a novel trap construction having particular utility in an intermittently operable pneumatic conveying system for solid polyethylene particles or the like, but which is also operable in a continuous system. The novel trap comprises an upstanding large volume cylindrical chamber having a top and a bottom, a first conduit for a particle-laden first stream of high-velocity gas having an outlet connected into the chamber at a position between the top and the bottom such that velocity is greatly reduced in the chamber. A second conduit leads from the chamber adjacent the top for conducting therefrom a second stream of highvelocity gas carrying solid particles. No other provisions for entrance or exit ofgas are necessary.

The second conduit has its entrance located below the top and spaced above the outlet of the first conduit, and both the first and second conduits have much smaller cross-sectional areas than the chamber so that the velocity is reduced sufficiently in the chamber to cause any heavy tramp metal particles and the polyethylene pellets to drop out ofsuspension and accumulate in the bottom of the chamber. The air velocity in the second conduit is sufficient to pick up polyethylene pellets from the central upper surface of the accumulation of polyethylene pellets and carry them from the trap. Any heavy tramp metal particles will remain in the lower portion of the chamber near the cylinder wall because of tangential location of the first conduit. The tangential inlet also provides a swirling action so that the polyethylene pellets will not bridge when the air supply is stopped.

THE DRAWING The invention will be described with reference to the drawings wherein:

FIG. 1 is a schematic diagram of a pneumatic conveying system embodying our novel trap;

FIG. 2 is an enlarged perspective view of the trap; and

FIG. 3 is a fragmentary vertical sectional view taken along the line 3-3 in FIG. 2.

THE PREFERRED EMBODIMENT Referring to FIG. I, there is shown a supply 11 of polyethylene particles in a silo l3 which has an outlet at the bottom connected to a conduit 15. A vent 17 in the top ofthe silo permits air to enter. Conduit 15 is connected into a cylindrical trap 19 at a position between the top 21 and the bottom 23 and is arranged to discharge its particle-laden air essentially tangentially to the trap. All particles in the air come to rest and accumulate in the trap. The exiting air leaves through a second conduit 25, carrying with it polyethylene pellets which have been picked up from the upper central surface of the accumulation through entrance 27 (which is located centrally within the trap a substantial distance below top 21 for assuring the presence of a high-velocity airstream at the entrance 27). Any tramp metal introduced to the trap will remain in the bottom near the cylinder wall.

The second conduit 25 leads to a receiver 29 at the point of consumption, containing a supply 31 of particles. When the supply 31 has built up to a predetermined level, a sensing device 33, such as a capacitance probe, acts through a control box 35 to stop a centrifugal suction fan 37 and the flow ofparticle-laden air stops. When the level of supply 31 drops a predetermined amount, device 33 restarts fan 37 to such more particle-laden air through the system.

Periodically (e.g., monthly) the accumulated tramp metal and residual polyethylene pellets should be removed from trap 19, during a period when the suction fan 37 is inoperative. A thumbscrew 41 is turned to disengage a threaded stem 43 from a threaded bore in a diametrical round crossbar 45 which is welded at its ends to the inner wall of the trap. Then bottom wall 47 is removed, permitting tramp metal and accumulated polyethylene particles to fall out. The round crossbar 45 provides a self-cleaning feature by eliminating a flat horizontal surface where particles could accumulate and not fall from the trap by gravity when the bottom is removed. Bottom wall 47 is then replaced and threaded stem 43 is reengaged with crossbar 45. An annular rubber gasket 49 provides a seal.

Effective intermittent operation without plugging has been secured with our novel trap construction when the conduits 1S and 25 have a 1% or 2-inch inside diameter, and trap 19 has an 8-inch inside diameter. The length of the trap is 1 /2 times its diameter, with conduit entrance 27 located below top wall 21 at a distance equal to one-fourth of the diameter, and with the outlet of conduit 15 below the middle of the trap at a distance from entrance 27 equal to three-fourths of the diameter. An airflow of cubic feet per minute through conduits 15 and 25 provides a minimum or terminal velocity of the pellets of 837 feet per minute; and a maximum velocity in the trap of 215 feet per minute. The polyethylene particles have a density of 35 pounds per cubic foot and a diameter generally between one-eighth and three-sixteenths inch (not necessarily spherical in shape). This trap will not operate satisfactorily unless the polyethylene pellets come to rest in the trap during the conveying period. The air velocity in this trap can be 20025O f.p.m., which is low enough to cause the pellets to leave the airstream and come to rest.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A method for separating tramp particles such as metal from a first stream of gas carrying in suspension therein particles ofa less dense material such as polyethylene, said method comprising conducting said first stream at high velocity; delivering said first stream tangentially into a chamber of sufficient size to reduce the velocity to a value such that both said tramp particles and said less dense material drop out of suspension and accumulate therein; reentraining particles of said less dense material with a second stream of high-velocity gas; withdrawing said second stream of high-velocity gas from said chamber at a locality spaced above the locality where said first stream enters said chamber; and intermittently interrupt- 2. A method in accordance with claim 1 wherein gas velocity in said chamber is between about 200 and 250 feet per minute.

3. A method in accordance with claim 1 wherein said first ing and then resuming the flow of said first and second streams 5 stream of gas carrying ParticleS is created by applying Suction without emptying said chamber between each interruption and resumption.

to a supply of said particles while admitting gas thereto. 

2. A method in accordance with claim 1 wherein gas velocity in said chamber is between about 200 and 250 feet per minute.
 3. A method in accordance with claim 1 wherein said first stream of gas carrying particles is created by applying suction to a supply of said particles while admitting gas thereto. 